Low and Very Low Birthweight Infants

Infants born with low weight face a number of serious health risks. In 2014, 8.0 percent of all newborns had low birthweight (less than 5.5 pounds), only slightly below the 2006 figure of 8.3 percent—the highest proportion on record.

Importance

Babies who have very low weight at birth (less than 1,500 grams, or 3.3 pounds) face infant mortality rates more than 100 times that of their heavier peers (more than 2,500 grams, or 5.5 pounds). Mortality among slightly heavier, but still low birthweight babies (between 1,500 and 2,499 grams) is much lower (13 per 1,000), though still 15 times higher than the mortality of babies who are born above that weight (2 per 1,000).[1] Risk factors for low and very low birthweight include multiple births (more than one fetus carried to term), maternal smoking, low maternal weight gain or low pre-pregnancy weight, maternal or fetal stress, infections, and violence toward the pregnant woman.[2]

Infants born at a low birthweight are also at increased risk of long-term disability and impaired development.[3] Infants born weighing less than 2,500 grams are more likely than heavier infants to experience delayed motor and social development.[4] Lower birthweight also increases a child’s likelihood of having a school-age learning disability, being enrolled in special education classes, having a lower IQ, and dropping out of high school.[5],[6] Risk for many of these outcomes increases substantially as birthweight decreases, with very low birthweight babies most at risk. Being born with a low birthweight also incurs enormous economic costs, including higher medical expenditures, special education and social service expenses, and decreased productivity in adulthood.[7],[8]

Trends

The percentage of infants who had low birthweight declined between 1970 and 1980, from 7.9 to 6.8 percent of all births, but increased slowly but steadily until 2006, when it was at 8.3 percent of births. Since then, the percentage has decreased slightly, to 8.0 percent of births in 2014. (Figure 1)

Research indicates that the overall increase in low birthweight rates is partly the result of an increase in multiple births after 1980,[9] though the rate of low birthweight among singleton babies increased as well. (Figure 1) In addition, improvements in technologies used to monitor at-risk pregnancies may have contributed to an increase in Cesarean section deliveries and the number of low-weight infant births.[10] The percentage of infants who are very low birthweight has increased slightly since 1980, but has stayed fairly consistent since the 1990s. (Figure 1)

Black infants are more likely than babies of other races to have low birthweight. In 2014, 13.2 percent of black infants had low birthweight, compared with 8.1 percent of Asian and Pacific Islander, 7.6 percent of American Indian and Alaska Native, 7.0 percent of white, and 7.1 percent of Hispanic infants. Black infants are also more than twice as likely as other infants to be of very low birthweight (2.9 percent in 2014, compared with between 1.1 and 1.2 percent among white and Hispanic infants, respectively). (Figure 2)

Among those of Hispanic origin in 2014, Puerto Rican infants were the most likely to have low birthweight (9.5 percent), while Mexicans and Central and South Americans were the least likely (6.6 and 6.7 percent, respectively). In 2013, the most recent year that information for Asian and Pacific Islander subgroups was available, Asian Indians were the most likely to have low birthweight (10.6 percent), followed by Filipinos (9.4 percent). Chinese were the least likely among Asians to have low birthweight children, at 5.9 percent. (Appendix 1)

Differences by Maternal Smoking Status

In 2014, 13 percent of infants born to cigarette smokers had low birthweight, compared with 7.5 percent of infants born to non-smokers, with similar differences seen in rates of very low birthweight. (Figure 3)

Differences by Plurality of Births

Infants that are singleton births are much less likely than those that are multiple births to have low birthweight. In 2014, 6.2 percent of singleton births had low birthweight, compared with 56.6 percent of births that were twin or higher plurality. Similarly, 1.1 percent of singleton births had very low birthweight, compared with 10.5 percent of other births. The proportion of non-singleton births that had low birthweight increased between 1990 and 2006, from 51.9 to 59.3 percent, but has since decreased slightly, to 56.6 percent. (Appendix 1) The proportion of singleton births that had low birthweight stayed at about six percent throughout the 1990s, but increased between 2000 and 2006, to 6.5 percent, but it has since fallen to 6.2 percent. (Figure 1)

International Estimates

National Goals

Healthy People 2020 includes a goal to reduce the percentage of low birthweight infants from 8.2 in 2007 to 7.8 by 2020, and the percentage of very low birthweight infants from 1.5 percent in 2007 to 1.4 percent by 2020.

What Works to Make Progress on This Indicator

Also, see Child Trends’ LINKS database (“Lifecourse Interventions to Nurture Kids Successfully”), for reviews of many rigorously evaluated programs, including the following which have been shown to be effective for minimizing negative outcomes for low birthweight infants:

Related Indicators

Definition

Low birthweight refers to infants weighing less than 2,500 grams (5.5 pounds), and very low birthweight refers to infants weighing less than 1,500 grams (3.3 pounds). Estimates are based on live births with known birthweight, and exclude stillborn births and live births with unknown birthweight.

Data Sources

Data for 2002-2013 and plurality data 1990-2013: Centers National Center for Health Statistics, National Vital Statistics System. VitalStats. Length of Pregnancy (Gestation) and Birthweight. Data for 1970-2001: National Center for Health Statistics. (2003). Health United States, 2003 with Chartbook on Trends in the Health of Americans. National Center for Health Statisti Table 12. Retrieved from http://www.cdc.gov/nchs/data/hus/hus03.pdf

Note: The race groups, white, black, American Indian or Alaska Native, and Asian or Pacific Islander include persons of Hispanic and non-Hispanic origin. Conversely, persons of Hispanic origin may be of any race.

1Excludes live births with unknown birthweight. Percent based on live births with known birthweight.

2 Trend data for Hispanics and non-Hispanics are affected by expansion of the reporting area for an Hispanic-origin item on the birth certificate and by immigration. These two factors affect numbers of events, composition of the Hispanic population, and maternal and infant health characteristics. The number of States in the reporting area increased from 22 in 1980, to 23 and the District of Columbia (DC) in 1983-87, 30 and DC in 1988, 47 and DC in 1989, 48 and DC in 1990, 49 and DC in 1991-92, and 50 and DC in 1993 and later years.

3Includes mothers of all races.

4Percent based on live births with known smoking status of mother and known birthweight. Due to changes in the birth certificate being adopted at different times across states, this includes as few as 45 percent of births (in 2007), and included 87 percent of births in 2013.

Sources: Data for 1970-2001: National Center for Health Statistics. (2003). Health United States, 2003 with Chartbook on Trends in the Health of Americans. National Center for Health Statistics. Table 12. Available at http://www.cdc.gov/nchs/data/hus/hus03.pdf. Data for 2002-2011 and plurality data 1990-2013: Centers National Center for Health Statistics, National Vital Statistics System. VitalStats. Length of Pregnancy (Gestation) and Birthweight..

Source: Centers for Disease Control and Prevention. (2015). Live births in the United States, 1995-2014. CDC WONDER Online Database. Available at https://wonder.cdc.gov/natality-current.html

[11]Estimates for specific race groups have been revised to reflect the new OMB race definitions, and include only those who are identified with a single race. Hispanics may be of any race, while estimates for blacks and whites do not include Hispanics.